The story of the Koreas, according to popular belief, begins on Mount Paektu - a mountain located on the China-North Korea border that is said to be the birthplace of Dangun, the mythical founder of what became Korea's first kingdom.
Thousands of years later, Kim Il Sung - the founder of North Korea - reportedly used the mountain as a hideout when fighting against the Japanese. His son, Kim Jong Il, was said to be born on those same sacred slopes - despite reports indicating he was in fact most likely born in Russia - and for decades since the mountain has been used to legitimise the Kim dynasty.
"Kim Jong Un became heir in his 20s despite having no achievements, solely because of the Paektu bloodline," Ryu Hyun-woo, an exiled North Korea diplomat, wrote in his book, Kim Jong Un's Secret Vault.
But the reality of Kim's maternal lineage paints a different picture.
Hundreds of miles away from Mount Paektu lies the city of Osaka: Japan's historical capital, and the place where Kim's mother, Ko Yong Hui, was said to be born.
From what biographers have pieced together, Ko was born in Osaka in 1952 to parents originally from Jeju Island, which sits off the southern coast of what is now South Korea.
As residents of Japan, Ko's family were "Zainichi Koreans": immigrants during Japan's 1910-1945 colonial rule of the peninsula.
But when she was about 10 years old, Ko's family emigrated to North Korea.
They were among the estimated 93,000 Koreans who moved to North Korea between 1959 and 1984, lured by a resettlement scheme that promised an idyllic life of free healthcare, education and jobs.
Migrants to the North were first viewed with envy as they brought cash, clothes and home appliances from the country's capitalist neighbour to the south.
But they were also labelled "jjaepo", a disparaging term for a group considered to be contaminated by foreign, dangerous ideologies.
North Korean society is deeply hierarchical, with some analysts comparing it to a caste system. And in this strict social classification - known as songbun – the jjaepo belong to the "wavering class", somewhere between the core and hostile classes.
They are subjected to heavy state surveillance and often denied admission to good universities or promising jobs.
"The [regime's] Paektu bloodline is seen as sacred," says Kim Hyung-su of the Northern Research Association. "So the idea of the leader being a jjaepo's son is unimaginable."
Ko managed to escape the fate of her fellow Zainichi Koreans, however, after she caught the attention of Kim Jong Il, who had already been groomed for succession.
Intelligence shows he was already wedded to Kim Young Sook, the daughter of a high-ranking military official, in a marriage hand-picked by his father. He was also known to have two other mistresses.
Despite this, Ko - a member of the elite Mansudae Art Troupe - was said to have caught Kim's attention due to her "natural beauty and dancing skills", says Yoji Gomi, a Japanese reporter who published a book on Ko in 2025.
Reports suggest that Kim fell passionately in love with Ko, and went on to have three children with her.
But children born out of wedlock face severe stigma in North Korea. And so, while Kim's official wife resided in the capital Pyongyang, Ko and her children were tucked 210km (130 mi) away in the coastal town of Wonsan.
Though she never married the supreme leader, and their union was not acknowledged by the regime, Ko managed to live what Gomi calls a "Cinderella-like life".
